Internet protocol radio dispatch system and method

ABSTRACT

A method and system for dispatching calls using a packet network is disclosed. The use of distributed call management modules, enables various communication systems, such as RF and PSTN systems, to communicate with each other over the IP network. Audio devices from the various communication systems are each assigned an IP multicast group. Distributed call management modules convert signals from the audio devices into IP packets and transmit the IP packets to designated IP multicast groups over the IP network.

FIELD OF THE INVENTION

This application relates to radio dispatch systems and methods.

BACKGROUND OF THE INVENTION

Public safety communication systems, such as 911 services, police andfirefighter systems, use radio dispatch. A constant in radio dispatchsystems is the need to position radio sites, consisting of RF receiversand transceivers, according to geographic topography. However, the calltakers are located elsewhere. For example, a 911 operator may be locatedat a PSAP (Public Service Answering Point). The radio sites aretraditionally interconnected with a number of point to point leasedlines creating a mesh of lines. The communication system is accessed byemergency personnel, such as police, firefighters and paramedics.Typically, dedicated public safety frequencies are used, which arefrequently in the 800 MHz FM range. Nomadic call takers are notsupported by these traditional systems.

In the aftermath of the event of Sep. 11, 2001, there is a mandate forthere to be interoperability between the communication systems of thevarious emergency services agencies. Traditionally, each agency operatesa private network, which is not programmed to access the frequencies ofthe other agencies. To make the traditional systems interoperable in atraditional manner, parallel lines are needed, as well as dedicatedinteroperable channels. The mesh of lines therefore gets morecomplicated.

Furthermore, each PSAP requires a backup. Using the traditional system,each backup requires its own set of leased lines, thus complicating themesh of lines even further.

Packet based networks are presently used for VoIP (Voice Over InternetProtocol) communications. These VoIP communications traditionally have acentral manager that runs the terminals.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a system and method forproviding radio dispatch capability using, in one exemplary embodiment,an Internet Protocol (IP) network, operator workstations, radiogateways, telephone gateways, and distributed call management functions.In accordance with some embodiments of the present invention,intelligence of the system is distributed across the system, providingscalability, fault-tolerance, and the ability to distribute networkelements, such as distributed call management modules (DCMM),geographically. Such geographic distribution allows optimization of thenetwork in contrast to using dedicated lines to connect to the radiosystem. Multipoint-to-multipoint communication is preferably enabled.Networks embodying the present invention can provide the ability toremote operator positions over the public Internet through, for example,virtual private networks.

In one aspect, there is provided a dispatch control system operable touse a packet network, to provide audio and signalling connectivity to aplurality of audio devices, the system comprising: a plurality ofdistributed call management modules, each distributed call managementmodule being adapted to serve a respective audio device and eachdistributed call management module having a respective group address foreach audio device; each distributed call management module operable toconvert audio and signalling from the respective audio device intopackets for distribution through the packet network using the respectivegroup address for receipt by any distributed call management modulesmonitoring the group address; and each distributed call managementmodule operable to monitor at least one selected group address by:receiving packets addressed to at least one selected group address andconverting such packets to audio and signalling for distribution to theaudio device.

In a second aspect, there is provided a distributed call managementmodule for use in a radio dispatch system, said distributed callmanagement module comprising: an audio processing engine for convertingan audio signal from an audio device to a packet signal; a call andmanagement processing engine for directing the packet signal to amulticast group address; and a packet processor for encoding the packetsignal as multicast packets and for decoding multicast packets from thepacket network, said packet processor configured to send and receivepackets over the packet network.

In a third aspect, there is provided a method of dispatching a callbetween audio devices, said audio devices being connected to a packetnetwork, said method comprising: assigning multicast group addresses toeach audio device; converting a call from a first audio device topackets; and transmitting the packets to the multicast group address ofthe first audio device.

Other aspects and features of the present invention will becomeapparent, to those ordinarily skilled in the art, upon review of thefollowing description of the specific embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference tothe accompanying diagrams, in which:

FIG. 1 is a block diagram of one exemplary dispatch system in accordancewith an embodiment of the present invention;

FIG. 2 is a block diagram of a distributed call management module inaccordance with an embodiment of the present invention;

FIG. 3 is a block diagram of one exemplary radio dispatch system inaccordance with an embodiment of the present invention;

FIG. 4 is a signal chart for a method of one embodiment of the presentinvention;

FIG. 5 is a flowchart of a method in accordance with an embodiment ofthe present invention;

FIG. 6 is a signal chart for a method of an embodiment of the presentinvention;

FIG. 7 is a block diagram of one exemplary radio site in accordance withan embodiment of the present invention;

FIG. 8 is a block diagram of one exemplary dispatch center in accordancewith an embodiment of the present invention;

FIG. 9 is a block diagram of one exemplary distributed call managementmodule in accordance with an embodiment of the present invention;

FIG. 10 is a block diagram of another exemplary dispatch system inaccordance with an embodiment of the present invention; and

FIG. 11 is a block diagram of one example of an exemplary dispatchsystem structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the systems and methods that follow, distributed call managementmodules operate as distributed aggregation and control points for radio,telephone, operator entities and any audio device. By using the modulesdistributed call management is enabled, as opposed to traditionalcentralized call management. A plurality of distributed call managementmodules is deployed over a packet network forming a distributed dispatchcontrol system. Calls from audio devices within the system are convertedto a packet network protocol, assigned an address and directed to theassigned address.

FIG. 1 is a block diagram of a dispatch system 900 provided by anembodiment of the present invention. Three audio devices 910, 912, 914are shown connected to a packet network 920 through three respectivedistributed call management modules 902, 904, 906.

While three audio devices and three distributed call management modulesare shown in FIG. 1, any number of audio devices and distributed callmanagement modules may exist in a dispatch system according to thepresent invention. As well, it is not necessary that there be onedistributed call management module for every audio device. In someembodiments, one distributed call management module may be responsiblefor more than one audio device. Also, an audio device may be connectedto more than one distributed call management module. Preferably, atleast one of the audio devices is a radio unit, and at least one of theaudio devices is an operator workstation, for handling calls from theradio unit.

The distributed call management modules 902, 904, 906 providedistributed dispatch call processing functionality as described indetail below. Each audio device 910, 912, 914 in the dispatch system 900is assigned a group address. Audio transmissions from each audio deviceare transmitted over the packet network to the associated group address.Any second audio device can monitor any first audio device'stransmissions by subscribing to the first audio device's group address.In some embodiments, there is also a status group address over whichstatus signals are sent. In some embodiments every distributed callmanagement module is a member of the status group and thus can monitorthe status data sent to the status group address. The status dataincludes all state changes, such as who is transmitting, the idle/busystatus of the various entities, etc.

Subscribers to each group address can monitor all transmissions by theaudio device to which the group address is assigned. For example ifaudio device 910 subscribes to the group addresses of the other twoaudio devices 912 and 914, audio device 910 can monitor alltransmissions from the other two audio devices.

To send audio, audio device 910 sends audio and signaling to distributedcall management module 902. The distributed call management module 902converts the audio to packets and sends the packets over the packetnetwork to the group address of the first audio device 910. For thepurpose of this example, the other two audio devices 912, 914 havesubscribed to the first audio device's group address. The distributedcall management modules 904, 906 responsible for the audio devices 912,914 receive the packets and convert them to an audio formatunderstandable by their respective audio devices. In embodiments wherethere is a status group address, status information in the signalingsent by audio device 910 may be converted to packets by the distributedcall management module 902 and sent to the status group address. In someembodiments real time status information is sent to the first audiodevice's group address along with the audio packets.

In some embodiments the group addresses are IP multicast groupaddresses. In some embodiments the multicast group address for eachaudio device is unique. An audio device, for the purpose of thisillustrative description, represents a communication resource within thesystem. For instance, an audio device may be an individual operatorworkstation that inputs one physical voice stream into the system atonce. Therefore in this example, a single operator represents a singleaudio device and is thus assigned a single IP multicast group address,regardless of however many entities listen in to this audio device.Similarly, in another example, each radio system inputs a finite set ofphysical voice streams within the system. In a frequency divisionmultiplex (FDM) system, the number of streams in a set is usually afunction of how many discrete carrier frequencies or channels areassigned to the radio system. Therefore in embodiments of the system ofthe present invention, each radio system would be assigned a finitenumber of IP multicast group addresses. In some embodiments, eachchannel in a radio system is assigned a multicast group address. Morethan one radio unit can use a channel. In that case, transmissions fromeach radio unit using a particular channel are converted to packets bythe distributed call management module responsible for the channel andsent on the multicast group address assigned to the channel. In someembodiments, the distributed call management module that transmits onthe multicast group address for a channel is also a member of themulticast group, meaning that radio units using the channel will alsohear audio of the other radio units using the channel. In this case, theradio units also receive their own audio, which may be muted to preventacoustic feedback. Preferably, the distributed call management module islocated at a radio station. Also, packets sent to the multicast groupaddress are converted to an RF signal, which is sent by the appropriateradio station to each radio unit using the channel. Furthermore, if aPSTN (Public Switched Telephone Network) is part of the dispatch system,each PSTN line within the dispatch system inputs one physical voicestream within the system, which as is true for the above examples, canactually be a summation of multiple subscriber streams if voiceconferencing techniques are utilized in the PSTN in the subscriberequipment. Therefore, each PSTN line would be assigned one IP multicastgroup address.

Therefore, the number of multicast group addresses is a direct functionof the number audio devices, plus one multicast group address used forstatus data exchange. Given that IP version 4 supports 2²⁸ individualmulticast group addresses, the system capacity permitted by this schemeis for all practical purposes infinite.

The dispatch system preferably utilizes the Internet Group ManagementProtocol (IGMP) defined in IETF RFC 2236, incorporated herein byreference, in distributed call management modules to controlsubscription to the multicast group addresses for purposes of receivingaudio and status multicasts. This subscription can be done, for example,dynamically for the audio multicasts, on an as-needed basis, derived bythe audio management method to be described in detail later. Use ofdynamic membership as per IETF RFC 1112, incorporated herein byreference, allows the system to utilize the IGMP pruning features of theIP network infrastructure to limit the packets coming into any givendistributed call management module to only those packets that areactually meaningful to that distributed call management module at thatgiven time, regardless of however many multicast packets exist in the IPnetwork.

Audio received by a distributed call management module from each audiodevice is taken from its “native” form, which is usually, but notlimited to, baseband analog audio, and vocoded using a configuredvocoder. Possible formats for packetizing the audio include G.711,G.723.1, G.729, GSM, IMBE and TETRA. The resulting audio packets aresent over the appropriate multicast group address preferably using RTP.Any distributed call management module needing access to an audio deviceperforms the opposite process by extracting the audio packets receivedover the multicast group address and decoding them back into theappropriate format, usually but not limited to baseband analog audio.

Preferably each individual audio device is statically assigned amulticast group address; multicasting towards this address is performedby the distributed call management module from which the audio actuallyoriginates. For instance, if a PSTN line is attached to a givendistributed call management module, this distributed call managementmodule originates multicast packets for this resource, which cancomprise a packetized version of the audio coming into the distributedcall management module from the PSTN line. When two audio devices are incommunication with each other, they each subscribe to the other'smulticast group and each multicast group address carries half of theconversation. For example, if audio device 910 is communicating withaudio device 912 in FIG. 1, audio device 910 subscribes to audio device912's multicast group and audio device 912 subscribes to audio device910's multicast group. Distributed call management module 902 convertsaudio from audio device 910 and sends it over audio device 910'smulticast group address. Distributed call management module 904 convertsaudio from audio device 912 and sends it over audio device 912'smulticast group address.

In some embodiments, all of the multicast group addresses are static andstored in a database, which can be accessed by the distributed callmanagement modules.

Many benefits result from the approach described herein. First,regardless of how many entities are present within the network, eachdistributed call management module need only be able to handle enoughsimultaneous multicast groups to support the maximum simultaneouscommunication requirements for that distributed call management module.For instance, if a system includes 100 PSTN lines, but an operator isonly required to support a 6-line conference, then the distributed callmanagement module supporting the operator needs only to support 6simultaneous multicast groups, in addition to the multicast group usedfor status data exchange.

This approach also drastically diminishes the bandwidth and processorrequirements of each individual distributed call management module andprovides much greater modularity compared to traditional, centralizedaudio processing approaches. This is because, for example, generallyoperational requirements for the maximum number of simultaneouscommunications per entity remain constant as entities are added to thesystem, as they are set by individual entity limitations (e.g. theability of a single operator to listen in to multiple conversationssimultaneously, or the ability of a PSTN line to support conferencing ofmultiple entities) rather than limitations by the number of resourcesaccessible.

As indicated above, preferably the audio devices include radio units andoperator workstations. Preferably, each operator workstationcontinuously monitors a plurality of radio channels; i.e. it ispermanently subscribed to the radio channels' multicast group addresses.By monitoring the status group address, an operator workstation is awareof all traffic taking place and can choose to join the appropriatemulticast group address in order to join in on an ongoing conversationusing a method that will be discussed below.

In a dispatch environment, a radio call on a radio channel is monitoredby multiple operator units. Preferably, the distributed call managementmodules have the functionality to decide which operator will handle agiven call, referred to hereinafter as “arbitration”.

FIG. 2 is a block diagram of an embodiment of a distributed callmanagement module 700 in accordance with the present invention. Thedistributed call management module does IP processing so that audiodevices can communicate over the IP network 20 using IP multicast groupsand IP packets. The distributed call management module comprises a callprocessing and management engine 710, an audio processing engine 720 anda packet processor 730. Audio interface 740 connects the audioprocessing engine 710 to an audio device 705. Signaling interface 735connects the call management and processing engine 720 to the audiodevice 705.

The call processing and management engine 710 and the audio processingengine 720 are shown connected in parallel between the packet processor730 and the audio device 705. However, this is for illustrative purposesonly. The functions represented by the call processing and managementengine 710, audio processing engine 720 and packet processor 730 aresimply a logical breakdown of the functions performed by the distributedcall management module 700. In some embodiments the audio processingengine 720 is subordinate to the call processing and management engine710. In some embodiments audio and signaling interfaces 740, 735 are onone line.

In other embodiments, the distributed call management module 700 alsohas a gateway connecting the call processing and management engine andthe audio processing engine to the audio device. The function of thegateway will be discussed below with reference to FIG. 9.

The distributed call management module 700 can be any combination ofhardware and/or software designed to implement the described functions.In some embodiments, the distributed call management module includes asoftware module operating on a personal computer. In other embodiments,the distributed call management module includes a software moduleoperating on a dedicated hardware module. The software module operateswith a graphical user interface in some embodiments.

Distributed call management modules can be located throughout a dispatchsystem, such as shown in FIG. 1. In some embodiments, there aredistributed call management modules located in radio sites and dispatchcenters. Distributed call management modules can also be located on anoperator workstation.

In some embodiments the distributed call management module interfaceswith the audio devices using MGCP or MEGACO protocols. The interface canalso be through interface cards located with a chassis in thedistributed call management module. In the case of virtual telephonelines, the distributed call management module can use H.323 or SIPprotocols over an IP network.

In operation, the packet processor 730 packetizes signals from the callprocessing and management engine 710 and the audio processing engine 720and transmits IP packets over the IP network 20. The packet processor730 also receives IP packets from the IP network and transmits them tothe audio processing engine 720 and call processing and managementengine 710, as appropriate.

The call processing and management engine 710 performs a controlfunction. The call processing and management engine 710 subscribes to IPmulticast groups and performs arbitration functions. In someembodiments, the call processing and management engine 710 also convertsstatus signals from the audio device for transmittal to a status IPmulticast group, having all of the distributed call management modulesin the system as members. Likewise, in some embodiments, status signalsreceived as IP packets from the IP network are converted by the callprocessing and management engine 710 to a form understandable by theaudio device.

In some embodiments, the call processing and management engine 710communicates with call processing and management engines in otherdistributed call management modules for the purpose of distributedcontrol of the system. The call processing and management engines of adispatch system collaborate to ensure that a failure of one distributedcall management module will not affect the operation of the dispatchsystem, apart from those components directly connected the particulardistributed call management module in which the failure took place. Insome embodiments, this is achieved by standby distributed callmanagement modules. For example, a radio station may be connected to amain and an alternate distributed call management module, with only oneconnection active at a time. If the main distributed call managementmodule fails, the radio station is switched over to the alternatedistributed call management module. In other embodiments, if onedistributed call management module fails, traffic is rerouted to anotherdistributed call management module and the affected distributed callmanagement module is put out of service.

The audio processing engine 720 provides an audio summation function. Ifa given audio device is subscribing to multiple multicast groups thatare transmitted simultaneously, the audio from these sources is summedand presented as a single audio signal to the given audio device. Theaudio processing engine also converts the audio signals from the audiodevice to an IP protocol signal and sends them to the packet processor730 to be packetized and sent to the IP network. The audio processor 720also converts signals from the packet processor 730 into audio signalsunderstandable by the audio device.

In the illustrative embodiments discussed herein, the method used by thedistributed call management modules connected to the IP network toexchange audio and status information comprises assigning an IPmulticast group address (RFC 1112) to be shared by the distributed callmanagement modules for status data exchange and a IP multicast groupaddress (RFC 1112) per separate audio device. This method enables theestablishment of point-to-point, point-to-multipoint ormultipoint-to-multipoint audio exchanges between entities.

The architecture of the systems described herein makes reconfigurationof any audio device possible without system interruption. As well,addition of another audio device is possible without systeminterruption. Also, the IP network can isolate any distributed callmanagement module without affecting the rest of the dispatch system.Restarting of any distributed call management module is possible withoutrestarting the entire dispatch system. Therefore, failure of any onedistributed call management module only affects the behaviour of thatparticular distributed call management module.

FIG. 3 depicts one exemplary radio dispatch system 10 in accordance withan embodiment of the present invention. The radio dispatch system 10comprises an IP network 20, radio sites 30 coupled to radio systems 40,dispatch centers 50 that include operator workstations 60, PSTN 70, apublic IP network 80, remote operator workstations 90, a radio unit 100,a telephony unit 110, which can be a wireline or a wireless unit, an IPradio system 120, an IP radio unit 130, a packet-based IP telephonenetwork 140, and an IP telephony unit 150. Distributed call managementmodules 35 are provided in the radio sites 30, distributed callmanagement modules 55 are provided in dispatch centers 50 anddistributed call management modules 95 are provided in remote operatorworkstations 90. The distributed call management modules 35, 55, 95provide distributed dispatch call processing functionality as describedherein. In some embodiments the IP network 20 is an ATM (AsynchronousTransfer Mode) network. In other embodiments the IP network 20 is aFrame Relay Network. In some embodiments, the radio systems 40 are landmobile radio systems. In some embodiments the public IP network 80 isthe Internet.

FIG. 3 shows a very specific example implementation of an embodiment ofthe invention. Other embodiments comprise any combination of audiodevices and distributed call management modules connected to an IPnetwork. For example, FIG. 3 shows two radio sites 30 connected to theIP network 20. In other embodiments any number of radio sites can beconnected to the IP network. Distributed call management modules 35 areshown in the radio sites 30. In other embodiments, the distributed callmanagement modules are not co-located with the radio site. For example,the distributed call management modules 35 can be located between theradio site and the IP network. FIG. 3 shows two radio systems 40 foreach radio site 30. In other embodiments, any number of radio systems 40can be connected to each radio site 30. FIG. 3 shows one radio unit 100in communication with a radio system 40. Any number of radio units 100may exist. FIG. 3 also shows one IP radio unit 130 and one IP radiosystem 120. It is understood that any number of IP radio units 130 andIP radio systems 120 are possible in other embodiments. Only one IPtelephony unit 150 and one packet-based IP telephone network 140 areshown. In other embodiments, any number of IP telephony units 150 andpacket-based IP telephone networks 140 are possible. As well, eachpacket-based IP telephone network 140 may be linked to a plurality of IPtelephony units 150. Two dispatch centers 50 are shown in FIG. 3. Anynumber of dispatch centers 50 is possible in other embodiments. Eachdispatch center 50 shown in FIG. 3 has two operator workstations 60 andone distributed call management module 55. In other embodiments thedispatch centers 50 can have any number of operator workstations 60 anddistributed call management modules 55. Furthermore, distributed callmanagement modules 55 can be located outside the dispatch centers 50.FIG. 3 also shows only one telephony unit 110 connected to PSTN 70. Anynumber of telephony units 110 can be connected to the PSTN 70. Likewise,any number of PSTN's can exist. The PSTN 70 is shown connected to twodispatch centers 50. The PSTN can be connected to the IP network throughany number of dispatch centers or through a distributed call managementmodule located exterior to a dispatch center. FIG. 3 shows two remoteoperator workstations 90 and one public IP network 80. Any number ofremote operator workstations 90 and any number of public IP networks 80are possible. The remote operator workstations 90 are shown havingdistributed call management modules 95 located on the workstations 90.Distributed call management modules 95 can be located exterior to theremote operator workstations 90. Although not shown, the system may alsoinclude a system manager capable of system maintenance, administrationand configuration. In some embodiments, the system is partitioned sothat any one audio source has access to only a defined subset of systemresources.

Preferably, the operators of the workstations 60 or 90 are monitoringall traffic from a number of radio channels. To achieve this, eachoperator subscribes to the IP multicast group of each channel it needsto monitor.

The example of FIG. 3 shows radio calls from radio units that are IPradio units and/or non-IP radio units. Some embodiments include onlynon-IP radio units. Other embodiments include only IP radio units. Thecapability to handle remote workstations connected to the public IPnetwork is included in the FIG. 3 embodiments. Other embodiments includeonly stationary workstations. Still other embodiments include onlyremote workstations. The telephony interfaces, shown in FIG. 3 are bothPSTN and IP-based. Some embodiments have only PSTN telephony interfaces.Other embodiments have only IP-based telephony interfaces. Otherembodiments have only radio interfaces and no telephony interfaces.

The following are specific examples of some of the types ofcommunication that are possible within the radio dispatch system of FIG.3.

Radio Call Example

Referring to FIG. 3, in operation, a radio unit 100 can initiate a radiocall, which can be a voice transmission, a data transmission or anycombination thereof. The call is routed via RF to radio system 40, thenthrough radio system 40 to a radio site 30. In the example shown in FIG.3, the communication between the radio system 40 and the radio site 30is over a physical circuit. The distributed call management module 35 atthe radio site 30 converts the radio call to IP packets for transmissionto and reception by entities connected to the IP network 20, using amethod to be described in detail later. The IP packets are transmittedby IP multicast or a similar mechanism that results in each packet beingforwarded to multiple destinations simultaneously. The distributed callmanagement modules of the audio devices that have subscribed to themulticast address, for example particular operator workstations 60 or90, will receive the packets and can then subsequently monitor the radiocall. Preferably, each radio channel is monitored by a respectiveplurality of operator workstations. For example, the call audio might bedirected to a headset or speaker and the call data can be displayed atsuch workstations.

Operator Workstation Example

In a further example, an operator of an operator workstation 60 or 90can initiate a radio call to a group of one or more radio units 100,which can be a voice transmission, a data transmission or anycombination thereof. Once again, the transmission is converted to IPpackets and the IP packets are sent over the IP network using IPmulticast or a similar mechanism to the one or more radio units. The IPpackets are routed by distributed call management module 55 or 95through the IP network 20 to one or more radio sites 30, wheredistributed call management modules 35 convert them to audio and datasignals. The audio and data signals are then directed by the distributedcall management modules 35 to the radio system 40 for broadcasting overthe RF network and receiving by radio units 100.

Telephony Unit Example

In yet another example a telephone unit 110 can initiate a telephonecall. As shown in the FIG. 3 embodiment, such call is routed through thePSTN 70 to the dispatch centers 50, where it is routed throughdistributed call management module 55. The routing from the telephoneunit 110 to the PSTN 70 can include the use of physical circuits. Thedispatch centers 50 determine the proper operator workstation 60 or 90to which to present the call, based on call distribution rules preset inaccordance with the mandates of the dispatch system. The operatorworkstation 60 or 90 can then be used to answer the call. Similarly, anoperator workstation 60 or 90 can place a call to a telephone unit 110through distributed call management module and the PSTN 70.

IP Radio Example

In the example shown in FIG. 3, a radio unit 130 on an IP radio system120 can initiate a radio call to a group of operators, which can be avoice transmission, a data transmission or any combination thereof. Sucha call can be routed via RF to radio system 120, then through to a radiosite 30, where the communication between the IP radio system 120 and theradio site 30 is over the IP network. The distributed call managementmodule 35 at radio site 30 converts packets received from IP radiosystem 120 to multicast packets and relays the IP packets from radiosystem 120 for processing by entities connected to the IP network 20,using a method to be described in detail later. This architecture allowsthe radio site 30 to operate with not only legacy systems such as radiosystems 40, but also IP radio systems 120, in which case instead of thehard-wired connection as between the radio system 40 and the radio site30, there is a virtual connection via the IP network 20 between the IPradio system 120 and the radio site 30. Any operator using an operatorworkstation 60 or 90 receiving the packets can then subsequently monitorthe radio call.

Operator Workstation to IP Radio Unit Example

In the exemplary embodiment shown in FIG. 3, an operator workstation 60can initiate a radio call to IP radio unit 130, which can be a voicetransmission, a data transmission or any combination thereof. Such acall can be routed through distributed call management module 55 to theIP network 20 to a distributed call management module 35 at a radio site30 to an IP radio system 120. The operator voice is then directed to theradio system 120 for broadcasting over the RF network and receiving byradio unit 130.

IP Telephony Unit Example

In the exemplary embodiment shown in FIG. 3, an IP telephony unit 150can initiate a telephone call. Such a call can be routed through the IPtelephone network 140 to the dispatch centers 50, using the IP network20. The distributed call management modules 55 at dispatch centers 50determine the proper workstation 60 or 90 to which to present the call,based on preset call distribution rules. The workstation 60 or 90 canthen be used to answer the call. Similarly, an operator workstation 60or 90 can select a telephone line on which to place a call to an IPtelephone unit 150 through IP telephone network 140.

The above mentioned scenarios are merely examples of the types ofcommunications that can be accomplished with the exemplary system.Depending upon implementation specifics, other combinations of audiodevices may also be connected, such as and without limitation:

Any combination of operator workstations can be connected together in anintercom call. An intercom call is a call between operators that doesnot go through telephone lines;

Any combination of operator workstations can be connected together withany combination of telephone lines to form a telephone conference;

Any combination of telephone lines can be connected together to form anunattended telephone conference;

Any combination of radio channels can be connected towards anycombination of operator workstations for the purpose of monitoring orlistening in to radio channels;

Any operator workstation can be connected towards any combination ofradio channels for the purpose of transmitting over radio channels;

Any combination of radio channels can be connected together in a radiopatch; and

Any combination of radio channels and any combination of telephone linescan be connected together in a telephone/radio patch.

Those skilled in the art will readily recognize that in addition to theabove example combinations, there are other combinations that can besupported by a system such as the one shown in FIG. 3.

Three Way Conference Example

In another example, to enable an operator sitting at an operatorworkstation to converse with a subscriber on a PSTN line, thedistributed call management module responsible for the workstationsubscribes to the IP multicast group for the PSTN line, and converts theIP packets to audio for the operator headset or speaker. In turn, thedistributed call management module responsible for the PSTN linesubscribes to the IP multicast group for the operator workstation, andconverts the IP packets to audio for transmitting towards the PSTN line.Thus all audio exchange between the two distributed call managementmodules is in the form of IP packets to two IP multicast groupaddresses, with half of the conversation carried by each IP multicastgroup address.

A second operator monitoring the status group address may decide to joinin the conversation. Alternatively, the first operator may invite thesecond operator to join. To enable a second operator to join theconversation, the distributed call management module responsible for thesecond operator workstation subscribes to the IP multicast group of thefirst operator workstation and the IP multicast group of the PSTN line,and combines the packets by audio summation techniques for transmissiontowards the second operator's headset or speaker. Simultaneously, thedistributed call management module responsible for the first operatorworkstation subscribes to the IP multicast group for the second operatorworkstation and sums the second operator workstation's audio with thePSTN line audio towards the first operator's headset or speaker, and thedistributed call management module responsible for the PSTN linesubscribes to the multicast group for the second operator workstationand sums the second operator workstation's audio with the first operatorworkstation's audio towards the PSTN line.

The signal chart of FIG. 4 shows an example of signaling to initiate thethree way conference of the last example. For the purpose of thisexample, only the audio signals are discussed. In some embodimentsstatus signals and status IP packets are also sent and received.

FIG. 4 shows signals being sent and received by a PSTN line 790, adistributed call management module 792 responsible for the PSTN line790, an operator workstation 796, a distributed call management module794 responsible for the operator workstation 796, another operatorworkstation 780 and a distributed call management module 798 responsiblefor the operator workstation 780.

As can be seen, an audio signal 761 from the first operator workstation796 to the PSTN line 790 is sent through the distributed call managementmodule 794, which converts the audio to IP packets. The distributed callmanagement module 794 sends the IP packets 763 over operator workstation796's IP multicast group address. The distributed call management module792 converts the IP packets to an audio signal and sends the audiosignal 764 to the PSTN line 790. Audio 765 from the PSTN line 790 issent back through the distributed call management module 792, where itis converted to IP packets 767. The distributed call management module792 sends a subscription signal 766 for the IP multicast group of thefirst operator workstation 796 and transmits the IP packets 767 to theIP multicast address of the PSTN line 790. The distributed callmanagement module 794 responsible for the first operator workstation 796receives the IP packets 767, converts them to an audio signal 768 andsends the audio signal 768 to the first operator workstation 796.

When the second operator workstation 780 requests to join or is invitedto join the conversation, a request signal 769 is sent through thedistributed call management module 798, which then sends a subscriptionsignal 770 for the IP multicast group of the PSTN line 790 and asubscription signal 771 for the IP multicast group of the first operatorworkstation 796. The distributed call management modules 792, 794 thensubscribe 772, 773 to the IP multicast group of the second operatorworkstation 780. Then audio 774 from the second operator workstation 780is converted to IP packets 775, 776 and sent to the second operatorworkstation 780's IP multicast group address. Preferably, IP packets 775and 776 are sent as a single packet using multicast techniques. The IPpackets 775 are received by distributed call management module 792 andconverted to audio signal 777 and sent to PSTN line 790. The IP packets776 are received by distributed call management module 794 and areconverted to audio signals 778 and sent to the first operatorworkstation 796.

In this example, audio from each of the three participants is broadcastto the other two participants, thus creating a three-way conferencecall. Any one of the operator workstation s or the PSTN line canunsubscribe from the IP multicast groups of the other two participantsat any time and the conversation between the other two participants cancontinue.

By using the method described above any number of audio devices cancommunicate with each other at any one time.

Another implementation of the present invention is a method ofdispatching a call in a dispatch system, such as a 911 dispatch system.In a 911 dispatch system, each operator is responsible for monitoring anumber of RF channels. In embodiments of the present invention, eachchannel has its own IP multicast group address. Furthermore, the presentinvention is not limited to RF channels. Any audio device with an IPmulticast group address can be monitored. Operators responsible formonitoring a particular channel subscribe to that channel's IP multicastgroup address. When an emergency call is received on one of thechannels, each operator who has subscribed to that channel's IPmulticast group will hear the call and can decide to respond or not.

A flowchart of an embodiment of a 911 dispatch method is shown in FIG.5. Audio/signaling for a call comes in to distributed call managementmodule Y from an audio device (Step 801). Distributed call managementmodule Y converts the audio/signaling to IP packets (Step 802).Distributed call management module Y then transmits the IP packets tothe IP multicast group associated with the audio device (Step 803). Thedistributed call management modules responsible for the operatorworkstations in the audio device's IP multicast group convert the IPpackets to a format understandable by their respective operatorworkstations (Step 804). The operator workstations can then receive theaudio.

Some operator workstations accept the call (Step 805). The acceptancesgo back through the distributed call management modules responsible foreach operator workstation to the distributed call management module Y.In the event multiple acceptances are received, distributed callmanagement module Y selects one operator workstation to take the call(Step 806). The distributed call management module responsible forchannel Y then sends a channel access grant to the selected operatorworkstation (Step 807). In some embodiments, channel access denials aresent to the other operator workstations that accepted the call. Thegrant and denials are processed by each operator workstation, and insome embodiments an appropriate indicator is generated in the form of anaudio or visual signal. The selected operator workstation is now free totransmit over the channel.

If the selected operator workstation wishes to broadcast to otherchannels, the distributed call management module responsible for theselected operator workstation subscribes to the IP multicast groups ofthe other channels and sends the IP packets to all of the distributedcall management modules responsible for the channels that the selectedoperator workstation chose.

In some embodiments, priorities for callers on a channel are set by anadministrative interface. The distributed call management moduleresponsible for a channel can do arbitration according to preset rulesto determine which caller is granted access. In some cases, a callerwith a higher priority can preempt a caller who is already using thechannel. In some embodiments, the distributed call management moduleresponsible for the channel can conduct this preemption function.

FIG. 6 is a signal chart for an example 911 call dispatch. FIG. 6 showssignals being sent and received by channel 850, distributed callmanagement module 852, distributed call management module 854, operatorworkstation 856, distributed call management module 858, operatorworkstation 860, distributed call management module 862 and operatorworkstation 864. Distributed call management module 862 is thedistributed call management module responsible for operator workstation864. Distributed call management module 858 is the distributed callmanagement module responsible for operator workstation 860. Distributedcall management module 854 is the distributed call management moduleresponsible for operator workstation 856. Distributed call managementmodule 852 is the distributed call management module responsible forchannel 850.

For illustrative purposes, it is assumed that the three operatorworkstations 856, 860 and 864 have subscribed to the IP multicast groupassociated with channel 850. As can be seen the call 820 comes in on thechannel 850 to distributed call management module 852. Distributed callmanagement module 852 converts the audio and signaling of the call to IPpackets and sends the IP packets 821, 822, 823 to the IP multicast groupof the channel 850. Preferably, IP packets 821, 822, and 823 are sent asa single packet using multicast techniques. Distributed call managementmodules 854, 858, and 862 receive the IP packets and convert them toaudio and signaling. The distributed call management modules 854, 858,and 862 send the converted signals 824, 825, 826 to their respectiveoperator workstations 856, 860 and 864. Operators 856 and 860 are shownsending acceptance signals 827, 829 to distributed call managementmodules 854 and 858 respectively. Operator workstation 864 is shownsending a rejection signal 831 to distributed call management module 862rejecting the call. Distributed call management modules 854 and 858convert the acceptances and send them to distributed call managementmodule 852 as IP packets 828 and 830, respectively. Distributed callmanagement module 862 converts the rejection signal to IP packets 832and sends the IP packets 832 to distributed call management module 852.Distributed call management module 852 then chooses an operatorworkstation to take the call 833. In this example operator workstation856 is chosen as the operator workstation to take the call. Next achannel access grant signal 834 is sent to distributed call managementmodule 854 along with a subscription to operator workstation 856's IPmulticast group. Distributed call management module 854 converts thesignal and sends the converted signal 835 to operator workstation 856. Achannel access denial signal 836 is sent to distributed call managementmodule 858, where it is converted. The converted denial 837 is sent tooperator workstation 860. Operator workstation 856 then commencestransmitting an audio signal 838. The audio signal 838 goes todistributed call management module 854, where it is converted to IPpackets 839 and sent to distributed call management module 852.Distributed call management module 852 converts the IP packets 839 to anaudio signal 840 and sends the audio signal 840 over channel 850.

In some embodiments, each operator workstation is monitoring a number ofchannels. An operator workstation can also transmit on the channelswhich the operator workstation is monitoring. To transmit to all thechannels, the operator workstation makes a request to each channel,indicating at the same time the operator workstation's IP multicastgroup address. When access is granted on a channel by channel basis,each channel subscribes to the operator workstation's IP multicast groupand transmission can begin at the same time. In some embodiments theacceptance signal is tied to a Push-to-talk switch, in which casearbitration takes place on a transaction by transaction basis. In otherwords, there is no arbitration for the entire call.

As mentioned earlier, distributed call management modules can bedistributed throughout a dispatch system. FIGS. 7 and 8 show distributedcall management modules located in a radio site and a dispatch center.Of course, distributed call management modules can be located in manyother locations.

FIG. 7 depicts one exemplary radio site in accordance with the presentinvention. In the FIG. 7 example, a radio site 31 comprises a pluralityof radio distributed call management modules 160, redundant IP switches170, and redundant IP routers 180. Radio distributed call managementmodules 160 are distributed call management modules designed tointerface between a radio system and an IP network.

The radio site 31 communicates with the radio stations 190 in the radiosystem 41 via radio interfaces 200. The radio distributed callmanagement modules 160 communicate with the IP switches 170 via LANconnections 210. In some embodiments the LAN connections 210 areEthernet connections. The IP switches 170 communicate with the IProuters 180 via redundant LAN connections 220. The IP routers 180communicate with the IP network 20 via redundant WAN connections 230. Invarious embodiments the WAN connections 230 can be ATM or Frame Relaylinks over copper, optical or wireless connections.

In the FIG. 7 example, when a radio call arrives at the radio site 30over a radio interface 200, it is processed by a radio distributed callmanagement module 160. The radio distributed call management module 160interprets the signaling of the radio call and converts the call statusdata to an IP packet and multicasts the IP packet to all distributedcall management modules of the system using a status multicast group. Insome embodiments the status multicast group is an IP multicast groupthat is subscribed to by all distributed call management modules and isused to multicast status changes. The radio distributed call managementmodule 160 also converts the audio to RTP (Real-time Transport Protocol)and sends it over the designated IP multicast group for the particularradio channel.

As will be recognized by those skilled in the art, the call signaling isradio system specific and can include combinations of “talk and listen”signaling such as call indication, advanced conventional signaling suchas unit ID, emergency, and trunked system signaling such as individualcall or unit status. As an example of the status conversion in theillustrative distributed system, status changes as a result of receivedsignaling are multicast to all distributed call management modules forthe distributed call management modules to update their local statusdatabase and subsequent presentation to an operator workstation.

Radio distributed call management modules 160 can also provide radiocalls over a radio interface 200, at the request of an operatorworkstation within the system for a non-operator-initiated transmission,such as a patch or radio repeat transmission. In such a case, thesignaling can be originated by the radio distributed call managementmodule 160 towards the radio interface 200, and the audio can be takenfrom its RTP form on an IP multicast group address and converted fortransmission towards the radio interface 200.

In the FIG. 7 example, the IP switches 170 serve as packet switches forthe radio site 30, by directing packets coming over the LAN connections210 and 220 from the radio distributed call management modules 160 androuters 180 to the destinations over the LAN connections 210 and 220.For instance, a radio distributed call management module 160 could sendan IP packet to a specific IP multicast group address, in which case anIP switch 170 would receive the IP packet on a LAN connection 210 andforward it on all LAN connections 210 and 220 that subscribe to the IPmulticast group.

In the FIG. 7 example, the WAN routers 180 serve to bridge the radiosite LAN with the IP network 20. To this end, they can performtranslation from the LAN protocol to the IP network protocol, as well asNAT (Network Address Translation) and firewall functions as appropriate.

FIG. 8 depicts one exemplary dispatch center 51 in accordance with thepresent invention. Dispatch center 51 preferably comprises redundant IProuters 240, redundant IP switches 250, a plurality of operatordistributed call management modules 260 serving operator workstations60, a plurality of telephone distributed call management modules 270operatively coupled via telephone lines 290 to an end office 280 that isin the PSTN 70. Operator distributed call management modules 260 aredistributed call management modules that interface between operatorworkstations 60 and an IP network 20. Telephone distributed callmanagement modules 270 are distributed call management modules thatinterface between a PSTN 70 and an IP network 20.

In the FIG. 8 example, the IP routers 240 and IP switches 250 preferablycommunicate via redundant LAN connections 300. The IP switches 250,operator distributed call management modules 260 and telephonedistributed call management modules 270 preferably communicate via LANconnections 310. The IP routers 240 communicate with the IP network 20via redundant WAN connections 320. In some embodiments, the WANconnections 320 are ATM or Frame Relay links over copper or opticalconnections.

In FIG. 8, the IP switches 250 serve as the packet switches for thedispatch center 51, by directing packets coming over the LAN connections300 and 310 from the WAN routers 240, telephone distributed callmanagement modules 270 and operator distributed call management modules260 to the destinations over the LAN connections 300 and 310. Forinstance, a telephone distributed call management module 270 could sendan IP multicast packet to a specific IP multicast group address, inwhich case an IP switch 250 would receive the packet on a LAN connection310 and forward it on all LAN connections 300 and 310 that subscribe tothis IP multicast group.

In FIG. 8, the telephone distributed call management modules 270terminate telephone lines 290 originating from the PSTN 70. These linescarry incoming and outgoing telephone traffic.

The operator distributed call management modules 260 provide the networktermination and call processing for the operator workstations 60.Operator workstations 60 can be used to receive and originate radiocalls, telephone calls, and intercom calls.

Whereas the description thus far distinguishes radio distributed callmanagement modules, telephone distributed call management modules andoperator distributed call management modules, this is merely forpurposes of explaining the system operation and does not form alimitation of the system. The distributed call management module shownin FIG. 9 performs all three functions.

FIG. 9 depicts one exemplary distributed call management module 320 inaccordance with the present invention. Distributed call managementmodule 320 comprises a call processing and management engine 330, anaudio processing engine 340, a packet processor 350 coupled to an IPnetwork 390 over a LAN connection 400, a radio gateway 360 coupled to aradio system 410 over radio interfaces 420, a telephone gateway 370coupled to the PSTN 430 over telephone lines 440, an operatorworkstation gateway 380 coupled to operator workstation 450 over theoperator interface 460. In some embodiments LAN connection 400 is anEthernet connection.

Referring to FIG. 9, signaling links 470 couple the gateways 360, 370,380, and the call processing and management engine 330; audio links 480couple the gateways 360, 370, 380, and the audio processing engine 340;control link 500 couples the call processing and management engine 330with the audio processing engine 440; data links 510 and 520 couple thecall processing and management engine 330, the audio management engine340, and the packet processor 350.

The radio gateway 360 provides a plurality of radio interfaces 420 toradio systems 410. One of the roles of the radio gateway 360 is toimplement the radio interface 420, which is dependent on the radiosystem 410. Thus, the gateway has the hardware and software to convertthe signaling and audio into and from packet form. In turn, the radiogateway 360 can terminate and originate the signaling required tocontrol the radio system 410, and can provide an interface to the callprocessing and management engine 330 for the control, over, for example,the interface 470. The radio gateway 360 can also convert the audio fromthe radio system 410 over the radio interface 420 to a form meaningfulfor exchange with the audio processing engine 340 over the link 480. Theradio gateway 360 also does the reverse conversion of signals from theaudio processing engine into audio in a form meaningful to the radiosystem 410. Details as the configuration of a radio gateway can be foundin the Applicant's co-pending United States application entitled “RadioGateway System and Method for Interfacing a Radio System and an IPnetwork” having Attorney Docket number 51742-1.

The telephone gateway 370 provides a plurality of telephone interfaces440 to PSTN 430. One of the roles of the telephone gateway 370 is toimplement the telephone interface 440, which is dependent on the PSTN430. In turn, the telephone gateway 370 can terminate and originate thesignaling required to control the PSTN 430, and can provide an interfaceto the call processing and management engine 330 for the control, overthe interface 470. The telephone gateway 370 can also convert the audiofrom the PSTN 430 over the telephone interface 440 to a form meaningfulfor exchange with the audio processing engine 340 over the link 480. Thetelephone gateway 370 also does the reverse conversion of signals fromthe audio processing engine into audio in a form meaningful to the PSTN430.

The workstation gateway 380 provides a plurality of workstationinterfaces 460 to workstation 450. One of the roles of the workstationgateway 380 is to implement the workstation interface 460, which isdependent on the workstation 450. In turn, the workstation gateway 380can terminate and originate the signaling required to control theworkstation 450, and can provide an interface to the call processing andmanagement engine 330 for said control, over the interface 470. Theworkstation gateway 380 can also convert the audio from the workstation450 over the workstation interface 460 to a form meaningful for exchangewith the audio processing engine 340 over the link 480. The workstationgateway 380 also does the reverse conversion of signals from the audioprocessing engine into audio in a form meaningful to the workstation460.

The call processing and management engine 330 performs similar functionsto the call processing and management engine 710 described withreference to FIG. 2. The audio processing engine 340 performs functionssimilar to the audio processing engine 720 described with reference toFIG. 2. The packet processor 350 performs functions similar to thepacket processor 730 described with reference to FIG. 2.

As will readily be recognized by those skilled in the art, multipleembodiments of the distributed call management module 320 are possible,where functions are implemented in software, hardware or a combinationthereof. For instance, the radio gateway 360, telephone gateway 370,operator gateway 380, call processing and management engine 330, audiomanagement engine 340 and packet processor 350 could all reside within asingle unit, with the operator workstation 450 residing in a separatephysical unit (e.g. personal computer). Alternatively, the operatorgateway 380, call processing and management engine 330, audio managementengine 340, packet processor 350 and operator workstation 450 couldreside within a single physical unit (e.g. personal computer), with theradio gateway and telephone gateway being separate physical units. Theseare only some of the many examples of other embodiments.

Of course, the dispatch system is not limited to the embodiments shownin FIGS. 1 and 3. Other embodiments are possible, due to the nature ofmulticast-enabled IP networks.

For instance, FIG. 10 depicts another exemplary dispatch system 530 inaccordance with the present invention. The FIG. 10 system preferablycomprises an IP network 20, a combined dispatch/radio site 540 thatincludes workstations 565, a radio system 40, a radio unit 100, a PSTN70, a telephone unit 110, a public IP network 80, a packet-based IPtelephone network 140, an IP telephony unit 150, two remote dispatchsites 550 and 560 that include combined distributed call managementmodule/workstations 580, and a mobile dispatch site 570 that includes amobile workstation 590.

In some embodiments the IP network 20 is a WAN and the public IP network80 is the Internet. In some embodiments the telephone units 110 arewireline units. In other embodiments they are wireless units. In stillother embodiments they can include both wireless and wireline units.

In operation, calls can be originated by any of the audio devices in thesystem of FIG. 10. The calls are converted by distributed callmanagement modules responsible for the audio devices according to amethod described above and sent as IP packets to an IP multicast groupaddress for the audio device that originated the call. The following areexamples of how calls are routed in the embodiment illustrated in FIG.10.

Radio Unit Call

A radio unit 100 can initiate a radio call, which can be a voicetransmission, a data transmission or any combination thereof, in whichcase the call is routed via RF to radio system 40, then through radiosystem 40 to the combined dispatch/radio site 540. Communication betweenthe radio system 40 and the radio site 540 can be over a physicalcircuit. As with the radio site 30 shown in FIG. 3, a distributed callmanagement module at the combined dispatch/radio site 540 can convertthe radio call to IP packets for processing by entities connected to theIP network 20, using a method such as described earlier. Any workstation565, 580 or 590 that has subscribed to the IP multicast group of radiounit 100 is subsequently able to monitor the radio call.

Operator Call

Any workstation 565, 580 or 590 can initiate a radio call to a radiounit 100, which can be a voice transmission, a data transmission or anycombination thereof, in which case the call is routed through thecombined dispatch/radio site 540 to a radio system 40. The communicationbetween the combined dispatch/radio site 540 and the radio system 40 canbe over a physical circuit. The operator voice is then directed to theradio system 40 for broadcasting over the RF network and receiving byradio unit 100.

Telephone Unit Call

A telephone unit 110 can initiate a telephone call, which is routedthrough the PSTN 70 to the radio/dispatch site 540, using, for example,common physical circuits. The distributed call management module atradio/dispatch site 540 can convert the telephone call to IP packets forprocessing by entities connected to the IP network 20, and determinesthe proper workstation 565, 580 or 590 to which to present the call,based on preset call distribution rules. The workstation 565, 580 or 590can then be used to answer the call. Similarly, an operator workstation565, 580 or 590 can select a telephone line to place a call to atelephone unit 110 through PSTN 70.

IP Telephony Unit Call

A IP telephony unit 150 can initiate a telephone call, which is routedthrough the IP telephone network 140 to the radio/dispatch site 540,using virtual circuits. The distributed call management module atradio/dispatch site 540 determines the proper workstation 565, 580 or590 to which to present the call, based on preset call distributionrules. The workstation 565, 580 or 590 can then be used to answer thecall. Similarly, an operator workstation 565, 580 or 590 can select atelephone line to use to place a call to a IP telephone unit 150 throughIP telephone network 140.

FIG. 11 depicts one example of an embodiment of the dispatch systemstructure shown in FIG. 10. Referring to FIG. 11, the radio/dispatchsite 540 includes redundant IP switches 175, redundant IP routers 185,combined operator/radio/telephone distributed call management modules600, and workstations 565. The radio/dispatch site 540 couples the endoffices 280 in the PSTN 70 via telephone lines 290, couples the radiobase stations 190 in the radio system 40 via radio interfaces 200, andcouples the IP telephone network 140 via the IP network 20. The IPswitches 175 and IP routers 85 are coupled via redundant LAN connections220. In some embodiments the LAN connections are Ethernet connections.The IP switches 175 and distributed call management modules 600 arecoupled via LAN connections 210. The IP routers 185 are coupled to theIP network 20 via redundant WAN connections 230, which in someembodiments are ATM or Frame Relay links over copper or opticalconnections. The workstations 565 are coupled to the distributed callmanagement modules 600 over links 610. In some embodiments these linksare physical links. In other embodiments they are virtual links whereworkstations 565 are coupled to the IP switches 175 and the connectionbetween the workstations 565 and the distributed call management modules600 is through the IP switches 175.

Remote dispatch site 550 includes redundant IP routers 245, redundant IPswitches 255, and workstations 580. In some embodiments, theworkstations 580 comprise combined operator distributed call managementmodules and workstations as described earlier. The IP routers 245 and IPswitches 255 are coupled via redundant LAN connections 305. The IPswitches 255 and workstations 585 are coupled via LAN connections 315.The IP routers 245 are coupled to the IP network 20 via redundant WANconnections 325.

Remote dispatch site 560 includes network access device 620 andworkstation 580. Examples of network devices 620 include DSL or cablemodems. Network access device 620 and workstation 580 can be coupled viaLAN connection 630. The network access device 620 can be coupled to theIP network 20 via WAN connection 640, using, for example, a virtualnetwork tunneled via the public IP network 80. In some embodiments theWAN connection 640 is a DSL connection. In other embodiments it is acable connection.

Remote dispatch site 570 includes mobile workstation 590, comprising anintegrated network access device. In some embodiments the mobileworkstation 590 is a laptop computer and the network access device is adial-up modem. Mobile workstation 590 can comprise a combined operatordistributed call management module and workstation as described earlieror it may be served by a distributed call management module 600 inradio/dispatch site 540. The mobile workstation 590 is coupled to thewide-area network 20 via WAN connection 640, using, for example, avirtual network tunneled via the public IP network 80.

In the FIG. 11 example, when a radio call arrives from the radio site 40over a radio interface 200, it is processed by the combinedoperator/radio/telephone distributed call management module 600, wherethe signaling is interpreted and converted to status changes multicastto all distributed call management modules over the status multicastgroup, and where the audio is converted to RTP and sent over thedesignated IP multicast group for the particular radio channel.

In the FIG. 11 system, operator/radio/telephone distributed callmanagement modules 600 can also originate radio calls over a radiointerface 200, at the request of an operator within the system or for anon-operator-initiated transmission, which in some embodiments is apatch or radio repeat transmission. The signaling is originated by theradio distributed call management module 600 towards the radio interface200, and the audio is taken from its RTP form on an IP multicast groupand converted for transmission towards the radio interface 200. Thedistributed call management modules 600 also terminate telephone lines290 originating from the PSTN 70. These lines can carry incoming andoutgoing telephone traffic. The distributed call management modules 600further provide the network termination and call processing for theoperator workstations 565. Operator workstations 565 can be used toreceive and originate radio calls, telephone calls, and intercom calls.

In the FIG. 11 example, the IP switches 175 serve a similar function tothe IP switches 170 in FIG. 7. The IP switches 255 serve a similarfunction to the IP switches 250 in FIG. 8.

The routers 185 serve a similar function to the routers 180 shown inFIG. 7. To this end, they can perform translation from the LAN protocol,such as Ethernet to a WAN protocol, such as ATM or Frame Relay, as wellas Network Address Translation (NAT) and firewall functions asappropriate. The routers 245 serve a similar function to the routers 240shown in FIG. 8.

The combined workstation/distributed call management modules 580 canprovide the network termination and call processing for the connectedoperator workstations, which can be used to receive and originate radiocalls, telephone calls, and intercom calls.

The network access device 620 serves to bridge the distributed callmanagement module/workstation 580 in remote dispatch site 560 to thenetwork 20. To this end, it can perform translation from the workstationprotocol, such as Ethernet to a WAN protocol, such as DSL or cable. Forremote dispatch site 560, as well as for the remote PSAP 570 case,Network Address Translation (NAT) and firewall functions can beperformed by the workstation 580 or 590.

The above embodiments have been presented to illustrate examples of thepresent inventions, and are not presented to limit the present inventionto any particular embodiment or structure discussed.

1. A distributed dispatch control system operable to use a packetnetwork, to provide audio and signalling connectivity to a plurality ofaudio devices, the system comprising: a plurality of distributed callmanagement modules, each distributed call management module beingadapted to serve a respective audio device and each distributed callmanagement module having a respective group address for each audiodevice; each distributed call management module operable to convertaudio and signalling from the respective audio device into packets fordistribution through the packet network using the respective groupaddress for receipt by any distributed call management modulesmonitoring the group address; and each distributed call managementmodule operable to monitor at least one selected group address by:receiving packets addressed to at least one selected group address andconverting such packets to audio and signalling for distribution to theaudio device.
 2. The distributed dispatch control system according toclaim 1, for use with the plurality of audio devices comprising at leastone radio unit and at least one operator workstation.
 3. The distributeddispatch control system according to claim 2, wherein at least one radiounit is an Internet Protocol based radio unit.
 4. The distributeddispatch control system according to claim 1 wherein at least some ofthe distributed call management modules serve multiple audio devices. 5.The distributed dispatch control system according to claim 2, whereineach distributed call management module serving an operator workstationis configured to monitor a plurality of group addresses each associatedwith a radio channel.
 6. The distributed dispatch control systemaccording to claim 2, wherein the at least one operator workstationcomprises at least one remote operator workstation connected over apublic network.
 7. The distributed dispatch control system according toclaim 1, wherein at least one audio device comprises at least onetelephony unit.
 8. The distributed dispatch control system according toclaim 7, wherein the at least one telephony unit is a PSTN (PublicSwitched Telephone Network) telephone unit.
 9. The distributed dispatchcontrol system according to claim 7, wherein the at least one telephonyunit is an IP (Internet Protocol) based telephony unit.
 10. Thedistributed dispatch control system according to claim 1, wherein eachdistributed call management module is operable to perform arbitrationfunctions for the audio device that the distributed call managementmodule is serving by: originating a call; receiving one or moreacceptances of the call from respective audio devices; selecting one ofthe audio devices to handle the call.
 11. The distributed dispatchcontrol system according to claim 2, wherein call processing for a calloriginated by a radio unit comprises: the distributed call managementmodule serving the radio unit transmitting packets for the call on therespective group address; at least one operator workstation monitoringthe respective group address; one or more of the operator workstationsresponding with an acceptance of the call; the distributed callmanagement module serving the radio unit selecting one of the one ormore operator workstations to handle the call.
 12. The distributeddispatch control system according to claim 1, wherein each distributedcall management module is operable to perform pre-emption functions forthe audio device that the distributed call management module is serving.13. The distributed dispatch control system according to claim 1,wherein each distributed call management module is operable todistribute status packets to a status group address, said status packetscontaining status information relating to the audio device that thedistributed call management module is serving.
 14. The distributeddispatch control system according to claim 1, further comprising thepacket network.
 15. The distributed dispatch control system according toclaim 14, wherein the packet network is an IP (Internet Protocol)network.
 16. The distributed dispatch control system according to claim1, further comprising the plurality of audio devices;
 17. Thedistributed dispatch control system according to claim 1, wherein therespective group addresses are IP multicast group addresses.
 18. Thedistributed dispatch control system according to claim 1, wherein eachdistributed call management module comprises a software module operatingon dedicated hardware.
 19. The distributed dispatch control systemaccording to claim 1, wherein each distributed call management modulecomprises a software module operating on a computer.
 20. The distributeddispatch control system according to claim 1, wherein each distributedcall management module comprises: an audio processing engine forconverting the audio and signalling from the respective at least oneaudio device to a protocol understandable by the packet network and forconverting signals from the packet network to audio and signallingunderstandable by the respective at least one audio device; a call andmanagement processing engine for directing the converted audio andsignalling to the respective group address; and a packet processor forencoding the converted audio and signalling as packets and for decodingpackets received from the packet network, said packet processorconfigured to send and receive packets over the packet network.
 21. Thedistributed dispatch control system according to claim 1, wherein thedistributed call management module is operable to convert said receivedpackets using MGCP (Media Gateway Control Protocol).
 22. The distributeddispatch control system according to claim 1, wherein the distributedcall management module is operable to convert said received packetsusing MEGACO (Media Gateway Control) protocol.
 23. The distributeddispatch control system according to claim 1, wherein the distributedcall management module is operable to convert said received packetsusing H.323 protocol.
 24. The distributed dispatch control systemaccording to claim 1, wherein the distributed call management module isoperable to convert said received packets using SIP protocol.
 25. Thedistributed dispatch control system according to claim 1, wherein thedistributed call management module is operable to convert said audio andsignalling using any one of G.711, G.723.1, G.729, GSM, IMBE and TETRAprotocols.
 26. The distributed dispatch control system according toclaim 1, wherein configuration of any audio device is possible withoutsystem interruption.
 27. The distributed dispatch control systemaccording to claim 1, wherein failure of any one distributed callmanagement module will only affect the operation of said faileddistributed call management module.
 28. The distributed dispatch controlsystem according to claim 1, wherein at least one audio device hasaccess to only a predefined subset of system resources.
 29. Adistributed call management module for use in a radio dispatch system,said distributed call management module comprising: an audio processingengine for converting an audio signal from an audio device to a packetsignal; a call and management processing engine for directing the packetsignal to a multicast group address; and a packet processor for encodingthe packet signal as multicast packets and for decoding multicastpackets from the packet network, said packet processor configured tosend and receive packets over the packet network.
 30. The distributedcall management module of claim 29, wherein the audio processing engineis also for converting a packet signal from the packet network into anaudio signal understandable by the audio device.
 31. The distributedcall management module of claim 29, wherein the call and managementprocessing engine also directs audio signals to the audio device. 32.The distributed call management module of claim 29 comprising a softwaremodule operating on dedicated hardware.
 33. The distributed callmanagement module of claim 29 comprising a software module operating ona computer.
 34. A method of dispatching a call between audio devices,said audio devices being connected to a packet network, said methodcomprising: assigning multicast group addresses to each audio device;converting a call from a first audio device to packets; and transmittingthe packets to the multicast group address of the first audio device.35. The method according to claim 34, further comprising: subscribing asecond audio device to the multicast group of the first audio device;converting a call from the second audio device to second packets;transmitting the second packets to the multicast group address of thesecond audio device.
 36. The method according to claim 35 furthercomprising: subscribing a third audio device to the multicast groups ofthe first and second audio devices; converting a call from the thirdaudio device to third packets; and transmitting the third packets to themulticast group address of the third audio device.
 37. The methodaccording to claim 34, further comprising converting the packets into aformat understandable by a second audio device.
 38. The method of claim34, wherein the assigning comprises assigning a unique IP multicastgroup address to each audio device.
 39. The method of claim 34, furthercomprising assigning a status IP multicast group address fortransmission of status information.
 40. The method of claim 34, whereinassigning the multicast group addresses comprises statically definingthe multicast group addresses.
 41. The method of claim 34, whereinassigning the multicast group address comprises assigning a separatemulticast group address to each audio device.